RV Solar Batteries, Inverters, Converters, and Mounts
An "RV system" (small boat and cabin systems are practically identical) can mean different things to different people. It might be just a small 5-watt panel that keeps the battery charged up between a few trips a year or over the winter. For someone living in one full time, it can mean 900 watts of panel (or all that will fit), a large battery bank, and an inverter. Nearly all solar panels are designed to withstand water and salt spray use, and all but the smallest have a 20 to 25-year warranty. Wind generators are common on sailboats and for remote homes, and we have sold a few to RV folks that tend to park a while.
After you have read this page, you might want to take a look at our "RV Solar - Frequently Asked Questions" page.
A complete schematic of a typical medium-sized cabin or remote home system. You can download the complete article (PDF) from HP Magazine.
Click on the picture for the full-sized image.
Most RV and boat lights and accessories run on 12 volts DC. These can all be easily powered by solar panels and batteries. You can reduce your power requirements, and the number of solar panels needed by switching to DC fluorescents, such as the "Thin-Lite" 12-Volt fluorescent lights - these put out the same light as incandescent, but draw less than one-third the power.
How many panels and the size of the batteries depends on how much power you use. If all you have is lights, a small TV, and the usual gizmos that come built in, around 80 to 130 watts of panels and a good heavy duty deep-cycle battery will probably do the job. If you plan on running an inverter for a microwave, coffee machine, vacuum cleaner, or other standard AC appliances you will need more, probably around 200 to 400+ watts of solar panel.
12 volt DC fluorescent lights are available, and a few other 12 volt appliances, such as ceiling fans - but as a general rule, 12-volt appliances are often of poorer quality and much more expensive than standard household appliances. Most RV's have some kind of inverter, ranging anywhere from the 250 watt or so for occasionally running small items, up to 4000-watt pure sine wave with a built-in battery charger.
Batteries
How much battery:
Battery needs will vary considerably but generally around 200 to 225 amp-hour capacity is considered the minimum for all but small RV's and trailer campers. Beyond that, it is often a question of space and a place to put any extra batteries. While you might "need" 800 amp-hours of capacity, if you only have room for half that, you will have to be more careful with your power usage.
Contrary to popular belief, two 6-volt batteries in series (golf cart size) are not better or any more reliable than a single large 12-volt, or two 12-volt batteries in parallel. At one time, there was some truth to the notion, because 6-volt golf cart batteries were the only commonly available deep cycle batteries. Regardless of which arrangement or size you use, it is important not to mix old with new batteries in a set, or to mix different types (especially gelled) with other types. If the age difference is more than a year between old and new batteries, it could cause problems - and more than 3 years usually a definite "bad thing". Most RV house battery systems should end up with around 200 to 600 amp-hours or more of battery storage capacity.
Gel-Cells: Some folks have had good luck with gelled cells, but our experience has been rather mixed. Gel-cells will NOT take as much abuse as standard flooded or AGM type batteries. One problem with gelled cells is that they are much more likely to be damaged by overcharging. We no longer sell gelled batteries.
You will probably want some kind of inverter. Large inverters should be as close to the battery bank as possible to avoid high cable costs and voltage drops.
You can get an approximate idea of how much battery you need (in amp-hours) by figuring out how many watts you need per day, and assuming that your batteries should be able to supply at least twice that much (you don't want to run your batteries totally dead). To figure watts, just multiply volts times amps - so a 12 volt light that pulls 3 amps will use 36 watts, and a 12 volt battery that can supply 100 AH will supply 12 x 100, or 1200 watts (however, if you pull the full 1200, your battery will be dead, so figure at least a 50% safety factor or 600 watts). For much more detailed info on batteries, go to our battery page. That same battery would run the 36 watt light for about 20 hours.
Inverters
Small inverters are pretty reasonable and will handle light loads - for example, a 75-watt inverter is enough to run small notebook computers. An inverter large enough to run the microwave (800-1200 watts) or coffee pot might run $500-$1100. The larger sine-wave inverters that put out 1000-4000 watts will be from $1000 to $2600. Most RV's and boats are happy with inverters in the 800 to 2500 watt range, with 1000 to 1500 watts being the most popular. With the panels, batteries, inverter, and other things needed for full time living a complete system might cost around $1800 to $5000. That size system may not be practical for some RV's and boats because not enough panels and/or batteries can be mounted in the area available. The most popular sized system consists of 150 to 300 watts of panel, a set of four to eight 6-Volt deep cycle batteries, a charge controller, and an 800 to 1500 watt inverter. For detailed info and specs, go to our inverter page. An inverter should ALWAYS have a fuse or breaker between the battery and the inverter - this is usually a "class T", or JJN or R type fuse (DC breakers are pretty expensive).
Hybrid Systems
Solar + Generator: Many people run a "hybrid" system. They use the solar for small loads, such as lights etc., that are needed all the time. With a small 250-800 watt inverter, they can run TV's, computers, and most other small appliances. They run a generator for the heavy loads. It might sound strange to have both, but the solar system saves having to run the generator all the time just for small loads, battery charging, or short-term heavy loads such as a microwave. Running a generator full time can get very expensive, and your neighbors get very upset. With a hybrid system, you might run the generator for an hour or two a week. With many hybrid systems, you can also use the generator to charge the solar system batteries through the inverter, in case you get a few cloudy days. The solar panels also ensure that the batteries remain at peak charge if the RV or boat is not used for long periods of time. A hybrid system, especially for boats, can also consist of a wind generator and solar panels. As a rough rule of thumb, 130 watts will cut the need to use the generator charger about 60 to 80%.
Converters
Converters are just another name for a battery charger. Most built-in converters that come from the factory with the RV will charge the batteries at about the same rate as 1 to 2 panels (3 to 10 amps), and usually have pretty poor regulation and charge characteristics (There are a few exceptions - some RV's are now coming with decent chargers, such as some of the Magnetek). Many put out too high a voltage after the batteries are charged, and will fry the batteries if left on continuously. Some battery manufacturers will not warranty batteries that are charged from a converter.
If you have anything more than a few bucks tied up in batteries, it may be best to trash the converter and rely on the solar panels and/or inverter with a good 3-stage charger, or get a well-regulated charger like the Iota charger. Small converters consist of little more than a step-down transformer and a rectifier. Since they have such a low output, it can take many hours or even days to fully recharge a large battery bank, it might take about 30-50 hours to recharge a single 200 AH battery bank from a small converter.
Mounts
For most RV systems we recommend the flat or "flush" mount. Tilting mounts are available and will give you about a 10-20% power increase under ideal conditions. However, most people find that the hassle of getting up on the roof and setting the mounts and making sure the RV is always parked so the panels can face due south is more of a hassle than it's worth unless you are going to be in one place for a long time. The tilting mounts cannot be left up when traveling. Nearly all tilting mounts will tilt either left or right.
It is best to mount any panel with a very slight tilt, 5% or less, so that you don't get standing water on the panel, and so that any rain will wash off the dust.
A typical medium usage RV or cabin system is listed below
- 1 or 2 80 to 150-watt solar modules, such as the Solartech SPM085 or Kyocera KD150.
- 1 - panel mounts for roof mounting.
- 1 - Morningstar solar charge controller
- 4 - 220 amp-hour 6-Volt deep cycle batteries (golf-cart size), or 2 Concorde 4D's
- 1 - 600 to 1500 watt inverter.
- The total cost can range from around $400 for a small "starter" system, up to $4,000 or more for a large system with a sine wave inverter. The average is around $900, but that can vary quite a bit.
The total energy output for this system is about 1600 watt-hours per day, which should run most standard RV lights and appliances with no problem, and will allow the use of small AC appliances. The approximate cost would be $1800 to $2300, depending on the exact components used. Starter systems begin as low as $400 for single panels. A starter system can be as simple as a single panel, mount, and charge controller.
Economics and Lifestyle Factors
There are two things to consider before buying a system for an RV - is it worth it, and why is it worth it?
The most obvious factor is the cost of the system - solar is not cheap, and may not be for everyone. It will save you generator fuel, wear, and maintenance - but probably not enough to be money ahead. Other things to consider is that solar is very quiet, and if installed correctly, is very low maintenance. The sound of a generator running in the wilderness or late at night in a camping area can get very annoying, and it is prohibited in many areas. It tends to make some folks very upset.
To find out if this is right for your situation, you need to figure out how much it will cost you to run the generator. An average generator will probably cost about $1 per hour to operate: if ran for 6 hours per day for one year, that would be about $2000, counting only fuel costs. Maintenance & repairs would add to that. At that cost, you would just about break even at twelve months with the system shown above. You may only run yours for an hour or two a day - if so, the payback (considering only the money) will be longer. To many, the noise, hassle, and fumes that generators produce is often far more important than just the dollar cost - although modern generators are much quieter than older ones, it is still a factor. Many places restrict generator usage, especially during the evening.
